1. Field of the Invention
This invention concerns self-supporting cores which, when framed produce sound-absorbing panels intended to be attached to indoor walls and ceilings of buildings.
2. Description of the Prior Art
It is often sought to diminish the noise level in indoor rooms, auditoriums, gymnasiums, restaurants, hallways, manufacturing plants and other indoor areas. Various types of sound-absorbing rigid panel products have been employed as ceiling tiles, and various rigid and soft wall coverings have been disclosed for sound absorption.
In general, prior sound-absorbing materials have either been difficult to install or have been deficient with respect to other requirements, such as physical properties and fireproof characteristics. Panels of framed rectangular construction have been fabricated of fiberglass batting for application to indoor room surfaces. Although fiberglass panels provide good thermal insulation, their acoustic absorption characteristics and aesthetic appearance are generally poor. Such panels are also easily susceptible to physical damage as a result of abrasion or impact, as by a ball.
Products made of "rockwool," sometimes called "mineral wool," have been employed in the building industry in the form of loose batting used for thermal insulation. Rockwool is generally produced by the centrifugal spinning of molten mineral magna. The resultant fibers, unlike fiberglass fibers, are of indeterminate length, and are intermingled as a loose batting resulting from their manner of production.
Batting products, whether of fiberglass or rockwool can have various bulk densities, depending upon the degree of compaction of the fibers, the specific gravity of the fibers, and the amount of binder which may be employed to impart dimensional stability to the structure. When the batting is formed into a shape-retaining self-supporting flat structure intended for use in the production of panels, that structure is often referred to as a "mat." As disclosed in parent application Ser. No. 08/398,868, mats of rockwool have been found to be vastly superior to mats of fiberglass with respect to acoustic absorption.
It has been found, however, that when a rockwool mat structure is of sufficient density to have good dimensional stability, it has poor acoustic absorption properties. Conversely, when the mat is of very low density, it is frail, having poor dimensional stability but having good acoustic absorption properties. Panels are made by causing a rigid frame to engage the rectangular perimeter of a mat, the mat now being referred to as the "core" of the panel. Although the frame imparts some structural stability to the overall panel construction, the frame in itself cannot correct problems inherent to frail cores. One problem of particular concern in panels employing frail cores is that sagging of the core will occur, especially in panels of 2 foot square size and larger. Other problems encountered with frail cores include: shedding of fibers, predisposition to forming permanent depression where compressively contacted by any object, and tearing during installation or subsequent handling.
It is accordingly an object of the present invention to provide a rectangular core structure for producing an acoustic panel having superior sound-absorbing characteristics.
It is another object of this invention to provide a core structure as in the foregoing object having acceptable characteristics relative to non-spreading of fire.
It is a further object of the present invention to provide a core of the aforesaid nature having superior compressive strength.
It is still another object of this invention to provide a core of the aforesaid nature having improved resistance to sagging.
It is yet another object of the present invention to provide a core of the aforesaid nature which produces a panel of pleasing appearance.
These objects and other objects and advantages of the invention will be apparent from the following description.